This invention relates to apparatus for use in magnetic inspection or testing procedures, and more particularly to devices especially suited to use in magnetic detection of faults in members or joints between members forming part of underwater structures.
The art of performing magnetic inspection tests on ferromagnetic structural members, particularly those tests wherein a member is subjected to a magnetic flux so that orientations of a plurality of magnetic particles can be observed as indicative of any of a variety of faults, has been extensively used. In the case of elongated test members, such as structural beams, tubes, or pipes, the magnetic flux has typically been induced in the member by means of an electrically energized coil or solenoid about the member, by application of permanent magnets to the member adjacent the zone to be inspected, or by causing a high amperage current to flow in the test member by application of current prods adjacent the weldment or other zone to be inspected. Where it is desired to use the electrical coil approach and the member is of substantial length or an end is inaccessible, it has been necessary to either manually wrap or wind a coil about the member or to use separable coil structures such as are illustrated in U.S. Pat. No. 2,439,827 to H. Sterenbuch, et al, and U.S. Pat. No. 2,895,103 to E. Vogt, et al.
While those expedients and devices are reasonably satisfactory for inspection and test procedures made under ordinary circumstances, they have been found to have serious shortcomings and disadvantages for use by divers in testing or inspection of underwater structures. In the case of manually wrapping a flexible cable around the test member, it is necessary for the diver to either make an underwater electrical connection of the free end to a power supply line or to have the free end hoisted to the surface for connection above water. The use of underwater connections has been found troublesome and dangerous to the safety and health of the diver, and the hoisting of the free end to the surface for each test requires that the diver handle inordinate lengths of cable in making the wrap. The mentioned separable coil devices, because of their make and break contacts or connections to form each coil turn, are wholly unsatisfactory for underwater use because of the conductive nature of the water medium, especially in the case of salt water and the fact that they may have to carry several hundred amperes of current. Both magnetic probes and current prods are limited because they produce only very localized magnetic fields rather than a predictable field throughout a weldment. Also, current prods, which typically transmit 1000 amperes or more, through bare contacts, present an extreme hazard to the diver and may cause deterioration of the steel member being inspected if arcing between the prod and the steel member occurs. Magnetic probes are, of course, less hazardous but may be unsuited to the particular geometries concerned. For example, the diver may be unable to inspect portions of a weld which lie in the acute angle formed between intersecting pipes or members of an underwater structure.